Frog in a well

First day it jumps 5 meters and falls 4 meters. Now it will be at a height of 1 meter.

Second day it jumps to 6 meters and falls back to 2 meter.

Third day it jumps to 7 meters and falls back to 3 meter.

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Fifteenth day it jumps to 19 meters and falls back to 15 meters.

Finally, sixteenth day it jumps to 20 meters, but now the frog have reached the top of the well.

So the Frog reaches the top of the well at the sixteenth day.

Since it is 20 meters deep, and the frog can jump (5 - 4) or 1 meter per day, and 5 meters at the last day. The answer is 15 + 1 = 16. Here are my steps: $\frac { depth\quad -\quad { jump\quad height }_{ max } }{ { jump\quad height }_{ min } } \quad =\quad \frac { 20\quad -\quad 5 }{ 1 } \quad =\quad 15$ Because each day the frog gets 1 meter higher, divide 15 with 1, you get 15 days. Add it with the last jump (5 meter) and you get 15 + 1 = 16